1. Field of the Invention
This invention relates to electronic musical instruments and more particularly relates to such instruments which are capable of playing multiple notes in response to the depression of a single key on a keyboard.
2. Description of the Prior Art
Certain keyboard instruments, such as a piano, have each of their keys assigned to a particular note or a pitch. For example, when the middle C key is depressed on a piano, only the middle C pitch is sounded by the piano strings. However, other keyboard instruments, such as pipe organs, traditionally have been able to play multiple pitches in response to the depression of a single key. This ability to vary the pitch represented by a keyboard key is implemented in pipe organs by providing a number of different ranks of pipes.
Normally, the pitch associated with a rank of pipes is given in terms of the number of feet of length of the average pipe in the rank. For example, an 8-foot rank of pipes may be pitched so that the playing of the middle C key on the keyboard (KC4) results in a pitch of about 256 Hz. In response to depression of key KC4, a 4-foot rank of pipes would produce a pitch one octave above middle C or 512 Hz. In response to depression of key KC4, a 2-foot rank of pipes would produce a note two octaves above middle C or 1024 Hz.
By properly coupling the ranks of pipes to the keyboard, notes having the pitches 256 Hz. (C4), 512 Hz. (C5) and 1024 Hz. (C6) can be simultaneously sounded by depressing a single key (e.g., middle C or KC4). Operating switches, normally referred to as stop tabs, are provided above the keyboard in order to couple the various ranks of pipes to the keys in the manner selected by the performer.
Two coupling methods generally evolved in the history of the pipe organ. According to the "straight" system of coupling, different ranks of pipes with different footages are provided in connection with each key of the keyboard. According to this "straight" system of coupling, the depression of the middle C key (KC4) could result in the pitches C4-C6 sounding in the manner previously described (e.g., by coupling 8-foot, 4-foot and 2-foot ranks of pipes to key KC4). Since separate ranks of pipes are associated with each key, the depression of the key one octave above middle C (KC5), could result in the sounding of pitches C5, C6 and C7. If either key KC4 or KC5 is depressed alone, pitch C5 is sounded by one pipe and pitch C6 is sounded by one pipe. If keys KC4 and KC5 are depressed together, pitches C5 and C6 each are sounded by two separate pipes, one associated with key KC4 and another associated with key KC5. In other words, the depression of key KC4 causes the sounding of two pipes corresponding to pitches C5 and C6 and the depression of key KC5 causes the sounding of two additional pipes corresponding to pitches C5 and C6, a total of four pipes. Naturally, pitches C5 and C6 are louder with four pipes sounding rather than two. As a result, if the performer depresses key KC4 with the 8-foot, 4-foot and 2-foot couplers operating, the depression of key KC5 with like couplers operating will result in a louder sound for pitches C5 and C6 than if the key were not depressed. This mode of operation is musically desirable, but requires a large number of pipes.
Due to the large number of pipes required in order to implement a straight coupling system, pipe organ builders also experimented with a "unified" system in which only a single rank of pipes of a particular footage is associated with a plurality of keys. According to the unified coupling system, depressing key KC4 with the 8-foot, 4-foot and 2-foot couplers operating also results in pitches C4, C5 and C6 sounding. However, the depression of key KC5 with the 8-foot and 4-foot couplers operating merely results in the continued sounding of the pipes representing pitches C5 and C6 which are already sounding as a result of the depression of key KC4. Thus, the depression of key KC5 results in no new or different sound and cannot be distinguished by the ear from the depression of key KC4 alone. Although the unified coupling system requires fewer pipes than the straight system, it is undesirable from the musician's point of view, because the depression of two keys sometimes sounds the same as the depression of a single key.
The straight and unified coupling systems used in pipe organs have been applied in principle to electronic musical instruments. Either the straight or unified coupling system could be used in connection with a keyboard of the type shown in FIG. 3 comprising keys 21-45 in which the pitch for an 8-foot coupler associated with a key is noted on each key. For example, key 21 corresponds to pitch C4 when played through an 8-foot coupler.
A fragment of an exemplary straight coupling system used in an electronic organ in connection with keys 21-45 is schematically illustrated in FIG. 1. Keys 21 and 33 operate switches S21 and S33, respectively. The straight coupling system also includes tone generators or keyers 50-55 which are capable of generating the pitches identified in FIG. 1. Each of the elements 50-55 can include a separate tone generator and keyer or can include a keyer provided with a tone signal from a tone generator which serves multiple keyers. The system also includes stop tab switches 57-59 corresponding to 8-foot, 4 foot and 2-foot couplers, respectively. By depressing key 21 with the 8-foot and 4-foot coupler switches 57 and 58 closed, pitches C6 and C7 sound. If key 33 is thereafter depressed, an additional pitch C8 sounds and pitch C7 sounds with increased loudness because it is being produced through the operation of generators or keyers 51 and 53. This operation is analogous to two pipes sounding at the same pitch.
A fragmentary unified coupling system used in an electronic organ in connection with keys 21-45 is schematically illustrated in FIG. 2. When key 21 is depressed, each of switches S218, S214 and S212 is closed; and when key 33 is depressed, each of switches S338, S334 and S332 is closed. The system also includes stop tab switches 57-59 corresponding to 8-foot, 4-foot and 2-foot couplers. Tone generators or keyers 50-52 and 55 are generating the pitches shown in the figure. Assuming switches 57 and 58 are closed (corresponding to an 8-foot and 4-foot coupler), the depression of key 21 will cause pitches C6 and C7 to sound. If, in addition, key 33 is depressed, an additional pitch C8 will sound, but pitch C7 will continue to sound with the same degree of loudness, even though it is selected for playing by the depression of both keys 21 and 33.
The straight system (FIG. 1) requires N times Y tone generators or keyers, and the unified system (FIG. 2) requires N plus Z keyers or tone generators, where N equals the total number of keys, Y equals the total number of stop tabs (or couplers) and Z equals the number of notes within the octaves encompassed between the highest and lowest stop tabs. For example, in the systems illustrated in FIGS. 1 and 2, assuming a 61 note keyboard, the straight system requires 183 keyers or tone generators (61 times 3), and the unified system requires 85 keyers or tone generators (61 plus 24, 24 notes being encompassed in the two octaves between the 8-foot and 2-foot stop tabs).
In summary, the straight system provides increased loudness for tones selected by more than one key, but only at the expense of a large number of tone sources or keyers.